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[ubuntu] Known that qemu 4.2 is incompatible with GCP instances?


I run tests with GCP instances as the OpenStack hypervisors.  Obviously
it's better if those can use libvirt_type kvm, i.e. nested virtualization,
and this has been possible prior to my current Ussuri upgrade work.

With Ussuri on Ubuntu, IIUC, we get qemu 4.2 from cloud-archive:ussuri, but
qemu 4.2 has a bug that was fixed by this commit prior to 5.0.0:
https://github.com/qemu/qemu/commit/4a910e1f6ab4155ec8b24c49b2585cc486916985

    target/i386: do not set unsupported VMX secondary execution controls

    Commit 048c951 ("target/i386: work around KVM_GET_MSRS bug for
    secondary execution controls") added a workaround for KVM pre-dating
    commit 6defc591846d ("KVM: nVMX: include conditional controls in
/dev/kvm
    KVM_GET_MSRS") which wasn't setting certain available controls. The
    workaround uses generic CPUID feature bits to set missing VMX controls.
[...]

The bug manifests on a GCP instance with nested virtualization enabled [1],
because such a GCP instance doesn't support MSR features.  The
OpenStack-level symptom is that a VM can't be scheduled onto that GCP
instance.

Is this a well-known problem?  For CentOS/RHEL, [2] looks similar and maybe
fixed, but it's difficult to be sure.

Best wishes,
    Neil

[1]
https://cloud.google.com/compute/docs/instances/enable-nested-virtualization-vm-instances
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1722360
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